Improvements in electrostatic relays

ABSTRACT

A relay is provided which includes a drop of conducting liquid, for example mercury, and means for subjecting the drop to an electro-static field to effect movement of the drop between at least two positions. This movement causes the conductive drop to interconnect different contacts, switching the relay from one state to another.

" United States Patent 15 3,670,130 Greenwood [4s] June13, 1972IMPROVEMENTS IN ELECTROSTATIC [56] References Cited RELAYS 2] I UNITEDSTATES PATENTS nvento h Ch i t r g S pher Greenwmd 2,545,669 3/1951Meyer ..200/1s2 x 2,830,159 4/1958 Varner.... [73] Assignee:International Standard Electric Company, 2.744.980 5/1956 y-- New York,NY. 2,802,918 8/l957 Boyle ..335/49 X [22] Filed: 1970 PrimaryExaminer-Herman J. Hohauser [21] Appl. No.: l3,450 Attorney-C. CornellRemsen, .lr., Walter J. Baum, Percy P. Lantzy, J. Warren Whitesel,Delbert P. Warner and James B.

Raden [30] Forelgn Application Priority Data March 7, 1969 Great Britain12,221/69 [57] ABSTRACT A relay is provided which includes a drop ofconducting [52] US. Cl ..200/183, 335/49,200/l8l liquid, for examplemercury, and means for subjecting the Int. Cl ...H01h 29/00, l-lOlh57/00 drop to an electrostatic field to etfect movement of the drop [58] Field of Search ..335/3, 49, 56; 200/ l 52, 9 between at least twopositions. This movement causes the conductive drop to interconnectdifferent contacts, switching the relay from one state to another.

21 Claims, 9 Drawing Figures PKTE'N'TEDJun 13 I972 3, 670. 1 39 sum 10F4 "IIIIIIIIIIIMVI Y /W 3 Inventor J. C. Greenwood 5 WXM AttorneyPATENTEDJUH 1 3 1972 SHEET 3 [IF 4 m w m PNENTED 1 3 1972 3,670,130

SHEET u or 4 1 IMPROVEMENTS IN ELECTROSTATIC RELAYS The inventionrelates to a relay.

The invention provides a relay including a drop of conducting liquid,and means for subjecting said drop to an electrostatic field to effectmovement of same betweenat least two positions, said movement causingthe relay to switch from one state to at least one other state. i

The foregoing and other features according to the invention will bebetter understood from the following description with reference to theaccompanying drawings, in which:

FIGS. 1A to IC diagrammatically illustrate the effects of anelectrostatic field on a drop of conducting liquid,

FIG. 2 diagrammatically illustrates a method of causing a drop ofconducting liquid to be moved in a plane by means of an electrostaticfield,

FIG. 3 diagrammatically illustrates a sectioned side elevation of onearrangement of the relay according to the invention,

FIGS. 4A and B respectively, diagrammatically illustrate a sectionedside elevation and a sectioned plan view of a modified version of therelay according to FIG. 3,

FIG. 5 diagrammatically illustrates a sectioned plan view of angtherarrangement of the relay according to the invention, an

FIG. 6 diagrammatically illustrates a sectioned side elevation of afurther arrangement of the relay according to the invention.

The surface tension of mercury is of the order of 4.6 X J.cm 'and adielectric film can be made that can store surface energies of thisorder, for example an anodized tantalum film can be made that can have acapacity of 0.1 11.] cm and will withstand a potential of 100 voltsapplied across it.

Now, the surface energy stored /2 cv".

The surface energy stored by an anodized tantalum film under theconditions cited above k X 10 X 10 J.cm 5 X 10 J.cm Referring to FIG.1A, a drop 1 of mercury is illustrated restmg on the surface of a film 2of tantalum oxide which is formed by anodizing the surface of a tantalummetal substrate 3 and under these conditions the shape of the drop isthat shape which has the minimum energy. As shown in FIG. 1A, the dropis in contact with an electrode 4 and out of contact with an electrode5.

When a voltage is applied between the drop 1 and the substrate 3, thesurface energy of the mercury where it is in contact with the dielectricfilm 2 is opposed by the energy in the electrostatic field which isgenerated by the applied voltage. The surface of the drop of mercury incontact with the tantalum oxide film 2 will therefore tend to increaseso as to increase the capacitances of the film and thus cause a changein the shape of the drop.

This effect, as illustrated in FIG. 1B, is used in a manner such thatthe drop makes contact with the electrode 5 and breaks the contact withthe electrode 4 when the drop is distorted by the electrostatic field.This arrangement can therefore form the basis of a relay having theadvantage that there is no contact wear due to switching the relay.

With this arrangement the returning force is the surface tension of thedrop which is unlikely to change with age and the drive power would bevery small. However, in the form illustrated such a relay has thedisadvantage that the input is capacitively coupled to the output, atleast in the on state, and is affected by gravity.

It was found by experiment that a dc. voltage applied between the dropand the substrate caused the drop to be distorted in a manner asoutlined in a preceding paragraph, but it was also found that the effectwas only a transient one i.e. the drop flattened out when the dc.voltage was applied but immediately returned to its original shape asillustrated in FIG. 1C. Also, when the capacitor formed by the drop 1,film 2 and substrate 3 is discharged, the drop momentarily flattens outagain.

It is thought that the drop immediately returns to its original shapedue to the fact that the surface of the tantalum oxide film 2 is capableof holding a charge in the absence of a conductor and that once the drophas transferred the charge to this surface, there is no longer any forceon it to retain the drop in its flattened form.

However, with an a.c. voltage applied between the drop and thesubstrate, the drop remains in its distorted or flattened form.

It should be noted that other conducting liquids for example gallium,indium, alkaline metals such as sodium/potassium compounds, ionicsolutions i.e. solutions of a salt in water, and mercury amalgams alsoexhibit the characteristics outlined in preceding paragraphs whensubjected to an electrostatic field. However, the use of gallium, indiumand alkaline metals is limited by temperature considerations since theyare only liquid at temperatures that may be inconveniently high. Also,the alkaline metals are highly reactive thereby giving furtherlimitations to their use. The main disadvantage of ionic solutions isthat they will react with the electrodes and cause them to corrodealthough the corrosion problem is minimized when the relay is operatedby an AC. voltage.

It should also be noted that the substrate 3 may be of metals other thantantalum, for example aluminum may be utilized in which case a film 2 ofaluminum oxide could be formed as the dielectric material by anodizingthe surface of the aluminum substrate.

Some of the above mentioned disadvantages can be avoided if theelectrostatic field is used to move the drop of conducting liquidinstead of distorting it in order to effect the switching of a relayfrom one state to at least one other state.

A method of causing a drop of conducting liquid to be moved in a planeby means of an electrostatic field is diagrammatically illustrated inthe drawing according to FIG. 2 wherein the drop 1 is illustratedresting on the surface of a film 2 of a dielectric material which isformed on a surface of two electrodes 6 and 7.

In operation, a voltage applied between the drop 1 and the electrode 7causes the surface energy of the drop where it is in contact with thatpart of the dielectric film 2 directly above the electrode 7 to opposethe energy in the electric field which is generated by the appliedvoltage.

The surface of the drop in contact with that part of the dielectric filmdirectly above the electrode 7 will therefore tend to increase so as toincrease the capacitance of this part of the film thereby causing thedrop to move in the direction of the arrow A. Conversely, if the voltageis applied between the drop 1 and the electrode 6 then the drop willmove inthe opposite direction to the arrow A. This arrangement cantherefore be used in a relay and has the advantage that the relay can bemade to latch and only consume power while it is switching from onestate to another. The fact that the drop of liquid returns to itsoriginal shape after switching is therefore of no significance.

Also, more complex types of switching can be achieved with thisarrangement, for example a drop of conducting liquid can be made to scanalong a number of contacts either sequentially or in any other desiredmanner. The relay diagrammatically illustrated in part in a sectionedside elevation in the drawing according to FIG. 3 utilizes this scanningfeature and basically includes within an insulating housing member 12, anumber of metal electrodes 8, for example of tantalum metal, a film 9 ofdielectric material, for example of tantalum oxide formed on a surfaceof each of the electrodes 8, a drop 10 of a conducting liquid which isin contact with the film 9, a number of metal electrodes 17 which aresecured to or formed in the inner surface of the housing member 12 and astrip contact 11 which is secured to or formed in the inner surface ofthe housing member 12 such that it is at all times in contact with thedrop 10 of conducting liquid. The housing member 12 for example ofglass, is provided with a series of depressions 16 which are arrangedsuch that each one of them is positioned directly opposite a separateone of the electrodes 8. Metal contact leads 13, 14 and are respectivelyprovided for the electrodes 8, the strip contact 11 and the electrodes17 which pass through and are secured in the walls of the housing member12.

In practice, the electrodes 8 and the strip contact 11 would beconnected to a voltage source (not shown in the drawing) respectively bymeans of the contact leads 13 and 14 in a manner such that a voltagepulse may be applied between the strip contact 11 and any one of theelectrodes 8. The elecby applying a voltage pulse between the stripcontact 11 and the electrode 8 situated below the right hand part of thedrop 10 illustrated in cross-hatched detail in FIG. 3. This causes thedrop 10 to move in the direction of the arrow B. The duration of thevoltage pulse is such that the surface of the drop 10 in contact withthat part of the dielectric film 9 directly above the electrode 8 viawhich the pulse is applied, increases by an amount sufficient to causeat least half the volume of the liquid content of the drop to bemovedpast the depression 16 which is situated on the right hand side of thedrop. When this state is reached the voltage pulse need not be sustainedsince the momentum of the dropwill be sufficient to cause it to latchinto the position indicated by the dotted line 18. Thus in order toeffect the movement in the opposite direction to the arrow B, thevoltage pulse of the required duration is applied between the stripcontact 11 and the electrode 8 situated below the left hand part of thedrop 10 illustrated in crosshatched detail in FIG. 3.

It can therefore be seen from the above that any desiredswitching'action can be achieved by causing the drop of conductingliquid to scan the electrodes 17 in a manner such that the desiredswitching action is effected, for example the electrodes' may besequentially scanned to effect a sequential switching action bysequentially applying voltage pulses between the strip contact 11 andthe electrodes 8.

A modified version of the relay is diagrammatically illustrated in FIGS.4A and 4B which show, respectively, a sectioned side elevation and asectioned plan view of the relay.

The construction and operation of this relay arrangement is basicallythe same as the relay according to FIG. 3 except that at each positionof the drop 20 two metal electrodes 21 are connected together, thearrangement of the electrodes 23 as illustrated in FIG. 4B is different,and a different latching mechanism for the drop 20 is utilized.

As illustrated in FIGS. 4A and 4B, the relay basically includes withinan insulating housing member 22 the wall of which is provided with anumber of protrusions 25, a number of metal electrodes 23, for exampleof tantalum metal each one of which is situated directly opposite aseparate one of the protrusions 25 a film 24 of dielectric material, forexample of tantalum oxide formed on a surface of each of the electrodes23, the drop 20 which is in contact with the film 24, the metalelectrodes 21, each one of which passes through and is secured withinthe wall of a separate one of the protrusions 25, and a strip contact 26which is secured to or formed in the inner surface of the housing member22 such that it is at all times in contact with the drop 20 ofconducting liquid. Metal contact leads 27 and 28 which are respectivelyprovided for the electrodes 23 and the strip contact 26 pass through andare secured in the walls of the housing member 22.

In practice, the electrodes 23 and the strip contact 26 would beconnected to a voltage source (not shown in the drawing) respectively bymeans of the contact leads 27 and 28 in a manner such, that a voltagepulse may be applied between the strip contact 26 and the electrodes 23.The electrodes 21 and the strip contact 26 would be connected to anoutput circuit or circuits (not shown in the drawing) in any desiredconfiguration.

In operation, the switching of the relay from one state to another stateis effected by causing the drop 20 to be moved in the same direction asor in the opposite direction to the arrow C such that after it has beenmoved it respectively occupies the position indicated by the chaindotted line 29 or the dotted line 30. I

The movement in the direction of the arrow C to achieve a switchingaction is efiected by first applying a voltage pulse between the stripcontact 26 and the electrode 23 situated below the left hand part of thedrop 20 illustrated in crosshatched detail in FIG. 4A, which will causethe drop 20, in a manner as previously described to move in thedirection of the arrow C. The duration of this voltage pulse is arrangedin conjunction with the shape of the electrodes 23 such that It causesthe surface of the drop 20 in contact with the dielectric film 24 toincrease by an amount such that part of the surface of the drop issituated directly above part of the electrode 2 3 which is adjacent tothe left hand end of the electrode 23 via which the voltage pulse isapplied i.e. the surface area of the electrodes 23 must overlap in theplane of movement of the drop in a manner such that the surface of thedrop can be influenced by the electrostatic field associated with oneelectrode 23 and while under this influence be situated above at leastpart of an adjacent electrode 23, situated in the direction of movementof the drop. After the application of the first voltage pulse a secondvoltage pulse should then be applied between the strip contact 26 andthe said ad acent electrode 23 which must be of sufficient duration tocause a continuation of the movement of the drop to a position where itwill latch into the position indicated by the chain dotted line 29.Since, as previously stated, the change of shape of the drop is atransient effect it is necessary for the second voltage pulse to beapplied immediately the duration of the first voltage pulse ceases oralternatively the two voltage pulses could be arranged to at leastpartially overlap each other. I Thus in order to effect the movement inthe opposite direction to the arrow C, a first voltage pulse of therequired duration should be applied between the strip contact 26 and theelectrode 23 situated below the right hand part of the drop 20,illustrated in cross-hatched detail in FIG. 4A, and then either duringor after the application of the first voltage pulse a second voltagepulse should be applied between 'the stri contact 26 and the electrode23 adjacent to the right hand end ofthe electrode 23 via which the firstvoltage pulse is applied.

In order to avoid the effects of gravityon the relay and the lack of,isolation between its input and output terminals, the relay arrangementdiagrammatically illustrated in FIG. 5 in a sectioned plan view may beutilized. With this-arrangement two equal sized drops 31 and 32 ofconducting liquid are utilized, each one of which is enclosed within anannular cavity 33, 34. The cavities 33 and 34 are interconnected bymeans of channels 35 and the motion of one of the two drops ofconducting liquid is transmitted to the other one of the two drops bymeans of a suitable electrically insulating inert fluid, for example aninert gas, contained within the channels 35 and that volume of each ofthe cavities 33 and 34 not occupied by the drops 31 and 32. Contactleads 37, 38 and 39 areformed in the wall of the cavity 34 by means ofwhich the switching action is effected and a contact lead 53 is formedin the wall of the cavity 33 which is utilized in conjunction withcontact electrodes 36 to effect the movement of the drop 31.

The drop 31 is caused to move from one end of the cavity 33 to the otherend thereof by means of an electrostatic field established between thedrop 31 i.e. via the contact lead 53 and either of the contactelectrodes 36. This movement causes the drop 32 to be moved therebyeffecting an interconnection between the contact electrode 37 and eitherthe contact electrode 38 or the contact electrode 39.

In practice, the relay illustrated in FIG. 5 can be quitesmall i.e. afew millimeters across and can therefore be manufactured in arraysutilizing photolithographic techniques. For such a manufacturing processthe starting material will be a flat insulating substrate for example ofglass, onto a major surface of which the metal contact electrodes 36,for example of aluminum, are deposited. A film of dielectric material,for example of silicon nitride is then formed over the electrodes 36 andthe remainder of the major surface.

The next stage of the manufacturing process involves the provision ofanother flat insulating substrate for example of glass having thecavities 33 and 34 and the channels 35 formed in one of the majorsurfaces thereof. The contact electrodes 37 to 39 and 53, in the form ofmetal wire, are next provided and fitted into the substrate such thatthey extend into the cavities 34 and 33 in the correct position i.e. theelectrodes 38 and 39 would be situated one at each end of the cavity 34,the electrode 37 would be situated in the center of the cavity 34 andthe electrode 53 would be situated in the center of the cavity 33, andsuch that they also extend from the other one of the major surfaces ofthe substrate to effect the connection thereto of an output circuit orcircuits.

The desired amount of conducting liquid is then metered into each of thecavities after which the two substrates are bonded together by asuitable adhesive in an inert liquid atmosphere such that the surface ofthe dielectric film is in contact with that major surface of thesubstrate having the cavities therein and the contact electrodes 36 arein register with the associated cavities. Since the bonding of the twosubstrates is effected in an inert fluid atmosphere the channels 35 andthat volume of each of the cavities 33 and 34 not occupied by the drops31 and 32 will contain the inert fluid and the adhesive must be capableof setting in the absence of air. However, the bonding of the twosubstrates need not necessarily be effected in an inert fluidatmosphere, the inert fluid could be metered into the channels 35 andthe unoccupied volumes of the cavities 33 and 34 after the bondingoperation in which case the adhesive need not necessarily exhibit theproperty of being capable of setting in the absence of air.

Alternatively, the substrate having the cavities therein can be formedby two flat insulting insulating substrates, one of which would haveapertures in the form of the cavities 33 and 34 formed therethrough andthe channels 35 which interconnect the cavities formed in one of themajor surfaces thereof. The other major surface of this substrate isthen bonded to the surface of the dielectric by a suitable adhesive suchthat the contact electrodes 36 are in register with the associatedcavities.

The other one of the two flat insulating substrates which would have thecontact electrodes 37 to 39, in the form of metal wire, fitted thereinsuch that they are located at positions corresponding to the positionsof the cavities 34 and such that they extend outwardly from each of themajor surfaces thereof is bonded to the major surface of the said one ofthe two substrates having the channels 35 therein by a suitable adhesiveafter the desired amount of conducting liquid had been metered into eachof the cavities. This bonding operation may be effected in an inertliquid atmosphere or the inert liquid could be metered into the channels35 and the unoccupied volumes of the cavities after the bondingoperation.

When the sandwiched structure of the array of relays is complete by anyone of the methods outlined in the preceding paragraphs the structure isthen divided up into the individual relays by a suitable cuttingoperation.

It should be noted that it is not an essential feature that the cavitiesshould be annular, they could in fact be in any elongated form.

Due to the small size and low power dissipation of this type of relaymuch higher packing densities than are achieved by its electromagneticequivalent can be obtained. Also on account of its small size andminimal drive requirements this type of relay is compatible withintegrated circuits and it could therefore share the same substrate assilicon chips and various thick and thin film elements.

cavity formed by a wall of dielectric With the relays outlined in thepreceding paragraphs, the relay contacts are at all times wetted withthe conducting liquid, for example, with the relays according to FIGS. 4and 5 a certain amount of conducting liquid is retained within thecavity protrusions that completely surrounds the relay contacts, thuswhen the drop of conducting liquid is moved between any two positions tocause the relay to switch from one state to another state, any flashingthat may occur due to this switching action will only result, in thecase of mercury, in the formation of mercury vapor since the flashingwill only occur between the drop of mercury and the mercury which wetsthe relay contacts. However, if the relay contacts are not wetted theflashing would result in the formation of a vapor of the material of therelay contacts thereby cause a certain amount of contamination.

A modified version of the relay outlined in preceding paragraphs canform part of a fluidic circuit. FIG. 6 diagrammatically illustrates onesuch arrangement wherein a drop 40 of conducting liquid is containedwithin a cavity 41 and in contact with a strip contact electrode 42formed in the cavity wall and a layer 43 of dielectric material formedon the surface of contact electrodes 44 and 45 contained within thecavity 41. Metal contact leads 46, 47 and 48 are respectively providedfor the electrodes 42, 44 and 45. An input pipe or channel 49 for thefluid input to the relay opens out into the cavity 41 and output pipesor channels 50 and 51 which also open out into the cavity 41 provide thefluid output ports for the relay.

As with the relay according to FIG. 3 the cavity 41 is provided with adepression 52 which is utilized to latch the drop 40 into its switchposition. In order to facilitate the operation of this relay in the samemanner as the relay according to FIG. 3 the surface area of theelectrodes 44 and 45 are arranged to overlap eg in a manner as shown inFIG. 4B, in the plane of movement of the drop such that the surface ofthe drop in the position illustrated in FIG. 6 can be influenced by theelectrostatic field associated with a voltage pulse applied between theelectrode 45 and the electrode 42. Similarly when in the other position,the surface of the drop can be influenced by the electrostatic fieldassociated with the voltage pulse applied between the electrode 44 andthe electrode 42.

In operation, the fluid input to the cavity 41, when the drop is in theillustrated position, passes out of the cavity via the output pipe orchannel 50. When it is required to direct the fluid output via the pipeor channel 51, the drop is moved in the direction of the arrow D in amanner as previously described until its takes up the other of its twopositions. When in this other position the fluid input passes out of thecavity via the output pipe or channel 51. It will be appreciated thatsuch a fluidic relay would only be capable of being operated in thepresence of relatively low pressure fluid since the pressure of thefluid must not be capable of distorting the shape of the drop by anamount such that it becomes out of contact with its drive electrode 44,45. Also the pressure exerted by the fluid must be capable of beingovercome by the electrostatic forces which are generated to effect themovement of the drop.

It will be appreciated that in the construction of the relays outlinedin the preceding paragraphs that it is not an essential feature that thefilm of dielectric material should bridge the gaps between theelectrodes on surfaces of which the film is formed. In practice theseelectrodes would be very closely spaced and the only requirement is thatthose surfaces of the electrodes exposed to the conducting liquid shouldbe covered with dielectric material in orderto efiect the most efficientcapacitive efiect.

It is to be understood that the foregoing description of specificexamples of this invention is made by way of example only and is not tobe considered as a limitation on its scope.

Iclaim:

l. A relay including a first drop of conductive liquid within amaterial, a plurality of flat metal plates forming capacitor platesimmediately outside one surface of the wall, the drop of liquidfunctioning as a capacitor plate within the wall, the drop of liquidresponding to electrostatic fields between respective ones of saidcapacitor plates and itself toefiect movement of the drop of liquid fromone position to another, said movement causing a loss of contact betweenat least one pair of relay contacts and the making of contact betweenanother pair of relay contacts, an inert fluid within said cavity in aspace between said first drop of conductive liquid and a second drop ofconductive liquid, said inert liquid forming means through which themovement of said first drop of conductive liquid is transmitted to andeffects the movement of the second drop of conductive liquid, a changeof position of said second drop causing changes in conductivity betweenadditional pairs of contacts.

2 A relay as claimed in claim 1 wherein the movement of said first dropis transmitted to said other drop by means of an electrically insulatinginert fluid.

3. A relay as claimed in claim 1 wherein said second drop iscontainedwithin another cavity each end of which opens into a separateone of the ends of said first mentioned cavity via an interconnectingpassage, said another cavity being provided with at least one relaycontact at each of a plurality of positions, each contact being securedto or formed in the inner surface of the cavity and being adapted, ateach of said positions, to make electrical contact with said seconddrop. I

4. A relay including a first drop of conductive liquid within a cavityformed by a wall of dielectric material, a plurality of metal platesforming capacitor plates immediately outside the wall, the drop ofliquid functioning as a capacitor plate, the drop of liquid respondingto electrostatic fields between respective ones of said capacitor platesand itself to efi'ect movement of the drop of liquid from one positionto another, said movement causing a loss of contact between at least onepair of relay contacts and the making of contact between another pair ofrelay contacts, an'inert fluid within said cavity in a space betweensaid first drop of conductive liquid and a second drop of conductiveliquid, said inert liquid forming means through which the movement ofsaid first drop of conductive liquid is transmitted to and effects themovement of the second drop of conductive liquid, a change of positionof said second drop causing changes in conductivity between additionalpairs of contacts, said capacitor plates being positioned on a majorsurface of a flat insulating substrate, said cavity and a pluralityofsupply and relay contacts, as'sociated therewith being formed in anothersubstrate, said another substrate being bonded to the surface of saidcommon layer when the dropsof conducting liquid have been metered intothe said cavities and the said electrically insulating inert fluidoccupying that volume of the said cavities not occupied by the saiddrops and the volume of the cavity interconnecting passages, and whereinelectrical contact leads for said supply contact, each of saidotherplates, and each of said relay contacts are provided.

5. A relay including a first drop of conductive liquid within a cavityformed by a wall of dielectric material, a plurality of metal platesforming capacitor plates immediately outside the wall, the drop ofliquid functioning as a capacitor plate,-the drop of liquid respondingto electrostatic fields between respective ones of said capacitor platesand itself to effect movement of the drop of liquid from one position toanother, said movement causing a loss of contact between at least onepair of relay contacts and the making of contact between another pair ofrelay contacts, an inert fluid within said cavity in a space betweensaid first drop of conductive liquid and a second drop of conductiveliquid, said inert liquid forming means through which the movement ofsaid first drop of conductive liquid is transmitted to and effects themovement of the second drop of conductive liquid, a change of positionof said second drop causing changes in conductivity between additionalpairs of contacts, wherein the capacitor plates are provided on a majorsurface of a flat insulating substrate, wherein said cavity is formed bypart of the surface of said common layer, an aperture formed in anotherflat insulating substrate such that it is in correct register with otherplates, and part of the major surface of a further flat insulatingsubstrate which is bonded to the other major surface of said anothersubstrate when the drops of conducting liquid have been metered into thesaid cavity and the said electrically insulating inert fluid occupiesthat volume of the said cavity not occupied by the said drops and thevolume of the cavity interconnecting passages and wherein electricalcontact leads for said supply contact, each of said other plates, andeach of said relay contacts are provided.

6. A relay as claimed in claim 1 including a plurality of cavitiesproviding a number of positions into which the drop of liquid may moveand including means for latching said drop into each of said positions.1

7. A relay as claimed in claim 6 wherein said latching means areprovided by increasing the cross-sectional area of the cavities at thepositions where said relay contacts and said supply contact are located.1

8. A relay including a drop of conductive liquid within a cavity formedby a sealed tube of dielectric material, said drop of liquid forming acapacitor plate, electrical supply contacting means terminating withinthe cavity and extending throughout the cavity parallel to the axis ofthe tube and through end walls of the tube to provide continuouselectrical contact with said drop, a plurality of capacitor platesaligned outside said cavity and along one side thereof, means forapplying potential across individual capacitor plates and said drop toproduce electrostatic fields, said electrostatic fields producingmechanical forces causing said drop of liquid to move from a positionnear a low electrostatic field to a position near a high electrostaticfield within the cavity, and at last one relay contact provided at eachof said positions, said relay contact being extended through the wall ofthe tube to a position enabling contact with the drop of liquid on aside of the tube opposite to the side along which the capacitor platesare aligned, each said relay contact being adapted at each of saidpositions to make electrical contact with said drop of conductive liquidwhen the drop is in a certain position.

9. A relay as claimed in claim 8 wherein electrical contact leads foreach of said relay contacts are provided which pass through and aresecured within the wall of said hollow insulat-- ing member.

10. A relay as claimed in claim 8 wherein said sealed tube of dielectricmaterial includes means for latching said drop into each of saidpositions. I

11. A relay as claimed in claim 10 wherein said latching means areprovided by reducing the cross-sectional area of the cavity formed bythe hollow insulating member at a point midway between said positions.

12. A relay as claimed in claim 11 wherein a single relay contact isprovided at each of said positions.

13. A relay asclaimed in claim 10 wherein said latching means areprovided by increasing the cross-sectional area of the cavity formed bythe sealed tube at two points at each of said positions.

14. A relay as claimed in claim 13 wherein two relay contacts areprovided at each of said positions, each of said relay contacts beinglocated at a point where the said cross-sectional area is increased.

15. A relay as claimed in claim 8 wherein the conductive liquid consistsof a material in the liquid state taken from a group of materialsincluding mercury, gallium, indium, alkaline metals, ionic solutions,and mercury amalgams.

16. A relay as claimed in claim 8 wherein the conductive liquid consistsof an alkaline metal in a sodium/potassium compound.

17. A relay as claimed in claim 8 wherein said common layer consists ofdielectric material takenfrom a group of materials including siliconnitride, aluminum oxide and tantalum oxide.

18. A relay as claimed in claim 17 wherein the said other plates consistof materials selected from aluminum or tantalum metal when said commonlayer is respectively of aluminum oxide or tantalum oxide.

19. A relay as claimed in claim 8 wherein the hollow insulating memberis of glass.

provided with at least one fluid outlet port at each of said positions,said drop being adapted when at each of said positions to isolate theoutlet port thereat from the said inlet port thereby directing the fluidinput to the other outlet port or ports of the relay.

1. A relay including a first drop of conductive liquid within a cavityformed by a wall of dielectric material, a plurality of flat metalplates forming capacitor plates immediately outside one surface of thewall, the drop of liquid functioning as a capacitor plate within thewall, the drop of liquid responding to electrostatic fields betweenrespective ones of said capacitor plates and itself to effect movementof the drop of liquid from one position to another, said movementcausing a loss of contact between at least one pair of relay contactsand the making of contact between another pair of relay contacts, aninert fluid within said cavity in a space between said first drop ofconductive liquid and a second drop of conductive liquid, said inertliquid forming means through which the movement of said first drop ofconductive liquid is transmitted to and effects the movement of thesecond drop of conductive liquid, a change of position of said seconddrop causing changes in conductivity between additional pairs ofcontacts.
 2. A relay as claimed in claim 1 wherein the movement of saidfirst drop is transmitted to said other drop by means of an electricallyinsulating inert fluid.
 3. A relay as claimed in claim 1 wherein saidsecond drop is contained within another cavity each end of which opensinto a separate one of the ends of said first mentioned cavity via aninterconnecting passage, said another cavity being provided with atleast one relay contact at each of a plurality of positions, eachcontact being secured to or formed in the iNner surface of the cavityand being adapted, at each of said positions, to make electrical contactwith said second drop.
 4. A relay including a first drop of conductiveliquid within a cavity formed by a wall of dielectric material, aplurality of metal plates forming capacitor plates immediately outsidethe wall, the drop of liquid functioning as a capacitor plate, the dropof liquid responding to electrostatic fields between respective ones ofsaid capacitor plates and itself to effect movement of the drop ofliquid from one position to another, said movement causing a loss ofcontact between at least one pair of relay contacts and the making ofcontact between another pair of relay contacts, an inert fluid withinsaid cavity in a space between said first drop of conductive liquid anda second drop of conductive liquid, said inert liquid forming meansthrough which the movement of said first drop of conductive liquid istransmitted to and effects the movement of the second drop of conductiveliquid, a change of position of said second drop causing changes inconductivity between additional pairs of contacts, said capacitor platesbeing positioned on a major surface of a flat insulating substrate, saidcavity and a plurality of supply and relay contacts associated therewithbeing formed in another substrate, said another substrate being bondedto the surface of said common layer when the drops of conducting liquidhave been metered into the said cavities and the said electricallyinsulating inert fluid occupying that volume of the said cavities notoccupied by the said drops and the volume of the cavity interconnectingpassages, and wherein electrical contact leads for said supply contact,each of said other plates, and each of said relay contacts are provided.5. A relay including a first drop of conductive liquid within a cavityformed by a wall of dielectric material, a plurality of metal platesforming capacitor plates immediately outside the wall, the drop ofliquid functioning as a capacitor plate, the drop of liquid respondingto electrostatic fields between respective ones of said capacitor platesand itself to effect movement of the drop of liquid from one position toanother, said movement causing a loss of contact between at least onepair of relay contacts and the making of contact between another pair ofrelay contacts, an inert fluid within said cavity in a space betweensaid first drop of conductive liquid and a second drop of conductiveliquid, said inert liquid forming means through which the movement ofsaid first drop of conductive liquid is transmitted to and effects themovement of the second drop of conductive liquid, a change of positionof said second drop causing changes in conductivity between additionalpairs of contacts, wherein the capacitor plates are provided on a majorsurface of a flat insulating substrate, wherein said cavity is formed bypart of the surface of said common layer, an aperture formed in anotherflat insulating substrate such that it is in correct register with otherplates, and part of the major surface of a further flat insulatingsubstrate which is bonded to the other major surface of said anothersubstrate when the drops of conducting liquid have been metered into thesaid cavity and the said electrically insulating inert fluid occupiesthat volume of the said cavity not occupied by the said drops and thevolume of the cavity interconnecting passages and wherein electricalcontact leads for said supply contact, each of said other plates, andeach of said relay contacts are provided.
 6. A relay as claimed in claim1 including a plurality of cavities providing a number of positions intowhich the drop of liquid may move and including means for latching saiddrop into each of said positions.
 7. A relay as claimed in claim 6wherein said latching means are provided by increasing thecross-sectional area of the cavities at the positions where said relaycontacts and said supply contact are located.
 8. A relay iNcluding adrop of conductive liquid within a cavity formed by a sealed tube ofdielectric material, said drop of liquid forming a capacitor plate,electrical supply contacting means terminating within the cavity andextending throughout the cavity parallel to the axis of the tube andthrough end walls of the tube to provide continuous electrical contactwith said drop, a plurality of capacitor plates aligned outside saidcavity and along one side thereof, means for applying potential acrossindividual capacitor plates and said drop to produce electrostaticfields, said electrostatic fields producing mechanical forces causingsaid drop of liquid to move from a position near a low electrostaticfield to a position near a high electrostatic field within the cavity,and at last one relay contact provided at each of said positions, saidrelay contact being extended through the wall of the tube to a positionenabling contact with the drop of liquid on a side of the tube oppositeto the side along which the capacitor plates are aligned, each saidrelay contact being adapted at each of said positions to make electricalcontact with said drop of conductive liquid when the drop is in acertain position.
 9. A relay as claimed in claim 8 wherein electricalcontact leads for each of said relay contacts are provided which passthrough and are secured within the wall of said hollow insulatingmember.
 10. A relay as claimed in claim 8 wherein said sealed tube ofdielectric material includes means for latching said drop into each ofsaid positions.
 11. A relay as claimed in claim 10 wherein said latchingmeans are provided by reducing the cross-sectional area of the cavityformed by the hollow insulating member at a point mid-way between saidpositions.
 12. A relay as claimed in claim 11 wherein a single relaycontact is provided at each of said positions.
 13. A relay as claimed inclaim 10 wherein said latching means are provided by increasing thecross-sectional area of the cavity formed by the sealed tube at twopoints at each of said positions.
 14. A relay as claimed in claim 13wherein two relay contacts are provided at each of said positions, eachof said relay contacts being located at a point where the saidcross-sectional area is increased.
 15. A relay as claimed in claim 8wherein the conductive liquid consists of a material in the liquid statetaken from a group of materials including mercury, gallium, indium,alkaline metals, ionic solutions, and mercury amalgams.
 16. A relay asclaimed in claim 8 wherein the conductive liquid consists of an alkalinemetal in a sodium/potassium compound.
 17. A relay as claimed in claim 8wherein said common layer consists of dielectric material taken from agroup of materials including silicon nitride, aluminum oxide andtantalum oxide.
 18. A relay as claimed in claim 17 wherein the saidother plates consist of materials selected from aluminum or tantalummetal when said common layer is respectively of aluminum oxide ortantalum oxide.
 19. A relay as claimed in claim 8 wherein the hollowinsulating member is of glass.
 20. A relay as claimed in claim 4 whereinsaid insulating substrates are of glass.
 21. A relay as claimed in claim8 wherein said drop is contained within a cavity in a manner such thatit is at all times in contact with the tube of dielectric material,wherein said cavity is provided with a fluid inlet port and wherein saidcavity is provided with at least one fluid outlet port at each of saidpositions, said drop being adapted when at each of said positions toisolate the outlet port thereat from the said inlet port therebydirecting the fluid input to the other outlet port or ports of therelay.